Find modulus of elasticity of the composite under isostrain:

A composite is made of alternate layers of 60% E-glass and 40% epoxy resin. If modulii of elasticity of E-glass and epoxy are respectively 72 GPa and 3 GPa, find modulus of elasticity of the laminated composite under isostrain and isostress conditions. Illustrate loading on sketch.

Solution

 (a)       Isostrain : Estrain  = V f E f  + Vm  Em

                                                         = 0.6 × 72 + 0.4 × 3

                                                          = 44.4 GPa

 (b)       Isostress : E_stress = E _f E_m /  V_fE_m+ V_mE_f = E _f /  V_f + V_m(E_f/E_m)

=          72 / (0.6 + 0.4 × (72/3)     = 7.06 GPa